"If you're living with a depressed person, it's pretty hard not to get depressed yourself." In your experience, is this true?

Someone said this to me a long time ago, and over the years I’ve had reason to think of it again and again. I think it was true for me.

Do you think it holds as a general rule?—If you live with someone else’s depression long enough, do you tend to lose your own buoyancy? Do you even begin to think of that state as normal?